Burned Area Emergency Response Tools

Details of FERGI Model

The FERGI model was developed by the U.S. Forest Service's Rocky Mountain Research Station, Boise Aquatic Sciences Lab (Luce 2001), and is based on several scientific research papers (Istanbulluoglu and others 2002; Istanbulluoglu and others 2003; Istanbulluoglu and others 2004; Luce 2005; Luce and others 2005; Rajagopalan and Lall 1999; Rhodes 2005; Shakesby and others, 2000). The FERGI model is a physically-based mathematical description of hillslope hydrologic and geomorphic response to a set of weather events, and the model is applicable to any part of the western United States. FERGI estimates the probability of post-fire rainfall excess (mm), runoff generation amount (m³ s^-1 m^-1), and gully initiation positions (m) on hillslopes with and without mitigations using contour felled logs/log barriers.

The FERGI model reports on the following:

• return inverval (yrs; from 1 to 100 years);
• rainfall excess no treatment (mm);
• ranfall excess treatment (mm);
• rainfall excess reduction (%);
• hillslope runoff no treatment (m³ s^-1 m^-1);
• hillslope runoff treatment (m³ s^-1 m^-1);
• hillslope runoff reduction (%);
• gully head no treatment (m);
• gully head treatment (m); and
• gully head reduction (%).

This output is provided as graphs (percent reduction of rainfall excess, hillslope runoff, and gully length) and tables of text file.

Weather Stations

Users can choose three nearest weather stations, which are wind, rainfall intensity, and COOP (Cooperative Weather Program; NOAA 2006) stations.

Depth to Water Repellent Layer (mm)

The proportion of the area that is underlain by water repellent soils after a fire.

Hillslope Length (m)

Average length of hillslope before flow begins to accumulate into channels.

Storage Capacity of Barriers (mm)

The amount of precipitation that can be stored by the barriers, i.e., the volume of water storage behind barriers divided by the total area over which the measured barriers are applied.

Fraction of Area Trenched (between 0 and 1)

The total length of scalping times the width of scalped area divided by the total area of the site.

Rainfall Excess, Post-Fire Runoff, and Gully Length

The model results are based on a rectangular strip with unit width.

Effectiveness of Contour Felled Logs/Log Barriers

The model provides the effectiveness as a function of storm return periods.

Does Not Provide Pre-Fire Results

No pre-fire results are available; therefore, users cannot compare pre- and post-fire changes.

Watershed Shapes

FERGI assumes a rectangular hillslope.

24-hour Storm Duration

FERGI considers only 24-hour storm duration; therefore, it is not applicable to the regions where the damaging storm duration is much shorter, such as 15 or 30 minutes.

REFERENCES

Istanbulluoglu, Erkan; Tarboton, David G.; Pack, Robert T.; Luce, Charles. 2002. A probablistic approach for channel initiation. Water Resources Research. 38(12): 1325.

Istanbulluoglu, Erkan; Tarboton, David G.; Pack, Robert T.; Luce, Charles. 2003. A sediment transport model for incision of gullies on steep topography. Water Resources Research. 39(4): 1103.

Istanbulluoglu, Erkan; Tarboton, David G.; Pack, Robert T.; Luce, Charles. 2004. Modeling of the interactions between forest vegetation, disturbances, and sediment yields. Journal of Geophysical Research. 109: F01009.

Luce, Charles H. (2001 September 5-copyright date). FERGI: Fire Enhanced Runoff and Gully Initiation model [Homepage of FERGI], [Online]. Available: https://fergi.boise.rmrs.fs.fed.us/fergi/ [2008 January 2].

Luce, Charles H.; Tarboton, David G.; Istanbulluoglu, Erkan; Pack, Robert T. 2005. Reply to comment by Jonathan J. Rhodes on "Modeling of the interactions between forest vegetation, disturbances, and sediment yields". Journal of Geophysical Research. 110: F01013.

Luce, Charles. 2005. Land use and land cover effects on runoff processes: fire. Encyclopedia of Hydrological Sciences. 13: 1831-1837.

Rajagopalan, B.; Lall, U. 1999. A k-nearest-neighbor simulator for daily precipitation and other weather variables. Water Resources Research. 35(10): 3089-3101.

Rhodes, Jonathan J. 2005. Comment on "Modeling of the interactions between forest vegetation, disturbances, and sediment yields" by Erkan Istanbulluoglu and others. Journal of Geophysical Research. 110: F01012.

Shakesby, R. A.; Doerr, S. H.; Walsh, R. P. D. 2000. The erosional impact of soil hydrophobicity: current problems and future research directions. Journal of Hydrology. 231-232: 178-191.

USDA Forest Service - RMRS - Moscow Forestry Sciences Laboratory
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